Designer Younicos claimed the unit was the first commercial battery power plant in Europe. It is located in Schwerin, northern Germany.
The battery unit is made up of 25,600 lithium-manganese oxide cells, supplied by Samsung SDI. The Japanese firm has guaranteed the cells' performance for 20 years.
The fully automated unit was designed to help wind power integration in to the grid.
"Our 5MW battery in Schwerin provides the same control power as a conventional 50MW turbine," said Clemens Triebel, chief technical officer of Younicos.
The unit was built for Wemag, a regional utility servicing the Mecklenburg region in northern Germany. Wemag said 80% of the power on its grid is supplied by renewable energy.
Younicos acquired battery specialist Xtreme Power in April following the US company going bankrupt.
Xtreme Power built the 15MW storage unit for the 30MW Kahuku wind project in Hawaii, which was destroyed by a fire in March.